Endometriosis is an extraordinarily complex, enigmatic chronic disease, although some investigators believe that some endometriotic lesions may be physiologic. Clinicians and scientists are unable to predict in which patients the endometriosis will progress to moderate, severe, or extensive disease. While the etiology, pathophysiology, and natural history of endometriosis are being studied, therapeutic trials with a “no-treatment” control arm are essential to discern treatment efficacy.
Sampson defined endometriosis as “the presence of ectopic tissue which possesses the histologic structure and function of the uterine mucosa. It also includes the abnormal conditions which may result, not only from the invasion of organs and other structures by this tissue, but from its reaction to menstruation.” In light of new immunologic, biochemical, and physiologic findings, this pathologic definition of endometriosis is no longer adequate. A functional definition is needed to reflect prognostic and therapeutic issues.
Traditionally, women with endometriosis were reported to be largely white, career-minded women of upper socioeconomic status who voluntarily delayed childbearing. This profile was based largely on convenient samples of women seeking treatment for infertility or pelvic pain associated with endometriosis. These early clinical studies did not fully adjust for biases arising from the selection of cases and other issues pertaining to medical care-seeking behaviors of affected women. More recent evidence suggests that endometriosis affects approximately 10% of women of reproductive age regardless of race, socioeconomic status, or childbearing intentions. Although limited in scope, findings from recent studies suggest that various factors may be associated with an increased or decreased risk of endometriosis, and these are summarized as follows.